ORCID Profile
0000-0003-4253-7167
Current Organisations
Texas A&M University
,
University of Queensland
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Publisher: Authorea, Inc.
Date: 22-12-2022
DOI: 10.22541/ESSOAR.167169649.93488411/V1
Abstract: In the absence of consistent meteorological data on Mars, the morphology of dunes can be employed to study its atmosphere. Specifically, barchan dunes, which form under approximately unimodal winds, are reliable proxies for the dominant wind direction. Here, we characterize near-surface winds on Mars from the morphology of barchans mapped globally on the planet by a convolutional neural network. Barchan migration is predominantly aligned with the global circulation: northerly at mid-latitudes and cyclonic near the north pole, with the addition of an anti-cyclonic north-polar component that likely originates from winds emerging from the ice cap. Locally, migration directions deviate from regional trends in areas with high topographic roughness. Notably, obstacles km such as impact craters are efficient at deflecting surface winds. Our database, which provides insights into planetary-scale aeolian processes on modern-day Mars, can be used to constrain global circulation models to assist with predictions for future missions.
Publisher: Scientific Societies
Date: 03-2022
DOI: 10.1094/PDIS-06-21-1256-RE
Abstract: Powdery mildew (PM), caused by two fungal species, Podosphaera xanthii and Erysiphe vignae, is a yield-limiting foliar disease commonly found in mungbean (Vigna radiata) cropping areas of the eastern region of Australia. Effective control of the disease relies largely on fungicide applications, mainly of the triazole group. Uncertainty in the current fungicide spray schedule recommendations, which advise commencing with a spray at the first signs of PM, prompted this study to evaluate PM severity and crop yield data obtained from fungicide trials, which also tested spray schedules starting before (early) or after (late) first signs, applied singly or combined with a follow-up spray. A meta-analytic approach was used to obtain mean differences of the PM severity and crop yield between plots sprayed with specific triazole-based spray schedules and nontreated plots. From 26 trials, 14 trials and 15 trials met the criteria for inclusion in PM severity and yield analyses, respectively. The schedule with the first spray starting at first sign, with a follow-up spray 14 days later, resulted in significantly lower disease severity compared with all other schedules. However, the yield protected was only numerically higher and not statistically different compared with single-spray at first sign, single-spray late, or two-spray starting late. PM severity and yield in the early sprayed plots did not differ from the nontreated plots. These findings support the current recommendations and provide additional evidence that yields are still protected when delaying the first spray up to a week after disease onset. They also suggest that additional sprays may not always be necessary, thus reducing direct fungicide costs, indirect costs related to fungicide insensitivity, and potential adverse effects to the environment.
Publisher: Scientific Societies
Date: 09-2022
Publisher: American Geophysical Union (AGU)
Date: 21-09-2023
DOI: 10.1029/2022GL102610
Publisher: American Association for the Advancement of Science (AAAS)
Date: 31-05-2013
Abstract: The Mars Science Laboratory spacecraft containing the Curiosity rover, was launched from Earth in November 2011 and arrived at Gale crater on Mars in August 2012. Zeitlin et al. (p. 1080 ) report measurements of the energetic particle radiation environment inside the spacecraft during its cruise to Mars, confirming the hazard likely to be posed by this radiation to astronauts on a future potential trip to Mars. Williams et al. (p. 1068 , see the Perspective by Jerolmack ) report the detection of sedimentary conglomerates (pebbles mixed with sand and turned to rock) at Gale crater. The rounding of the rocks suggests abrasion of the pebbles as they were transported by flowing water several kilometers or more from their source.
Publisher: Wiley
Date: 03-11-2010
Publisher: Springer Science and Business Media LLC
Date: 10-03-2023
DOI: 10.1007/S10658-023-02664-5
Abstract: Powdery mildew of cucurbits, caused by Podosphaera xanthii , is an economic constraint in cucurbit production worldwide. This study examined the influence of temperature and vapour pressure deficit (VPD) on the rate of conidial germination and the formation of germ tubes in an Australian P. xanthii isolate 12 – 48 h after inoculation. Two experiments were prepared by inoculating cucumber, cv. crystal salad, leaf-discs using a spore settling tower. The first experiment incubated inoculated cucumber leaf-discs at eight temperatures between 8 and 35 °C under saturated vapour pressure (SVP), the second compared 18 VPD conditions between 0.038 and 1.797 kPa, in six humidity chambers (33% – 99% relative humidity) and three temperatures (22 °C, 25 °C, 28 °C). Leaf-discs were cleared, stained and microscopically inspected for conidial germination and the number of germ tubes. The optimal temperature for germination was 28ºC at SVP, where more than 50% of conidia had germinated by 12 h, and 85% by 48 h. Fewer germinated conidia were recorded after 12 h at other temperature treatments between 17 °C and 31 °C. The germination percentage and germination rate were significantly lower when vapour pressure was between 0.13 and 2.5 kPa, with germination in response to VPD varying by approximately 10%, indicating difficulty associating conidial germination to VPD above 0.13 kPa. Germ tube production was highest between 25 ºC and 28 ºC at the lowest VPD treatment at near SVP, with more than 50% of the germinated conidia producing at least three germ tubes. Germination and formation of germ tubes significantly reduced when VPD increased. P. xanthii conidia were able to produce a primary germ tube under relatively dry conditions, such as 2.53 kPa, but these results show infection would be less likely and require longer incubation. This study provides the first crucial step in simulating powdery mildew infections on cucurbit plants and may lead to a model capable of providing risk forecasts or fungicide management decision support tools.
Publisher: Springer Science and Business Media LLC
Date: 08-10-2020
Publisher: American Association for the Advancement of Science (AAAS)
Date: 27-09-2013
Abstract: “Jake_M,” the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the Curiosity rover, differs substantially in chemical composition from other known martian igneous rocks: It is alkaline ( % normative nepheline) and relatively fractionated. Jake_M is compositionally similar to terrestrial mugearites, a rock type typically found at ocean islands and continental rifts. By analogy with these comparable terrestrial rocks, Jake_M could have been produced by extensive fractional crystallization of a primary alkaline or transitional magma at elevated pressure, with or without elevated water contents. The discovery of Jake_M suggests that alkaline magmas may be more abundant on Mars than on Earth and that Curiosity could encounter even more fractionated alkaline rocks (for ex le, phonolites and trachytes).
Publisher: American Geophysical Union (AGU)
Date: 14-09-2020
DOI: 10.1029/2020GL088773
Abstract: Aeolian dune fields are self‐organized patterns formed by wind‐blown sand. Dunes are topographic roughness elements that impose drag on the atmospheric boundary layer (ABL), creating a natural coupling between form and flow. While the steady‐state influence of drag on the ABL is well studied, nonequilibrium effects due to roughness transitions are less understood. Here we examine the large‐scale coupling between the ABL and an entire dune field. Field observations at White Sands, New Mexico, reveal a concomitant decline in wind speed and sand flux downwind of the transition from smooth playa to rough dunes at the upwind dune‐field margin, that affects the entire ∼ 10‐km ‐long dune field. Using a theory for the system that accounts for the observations, we generalize to other roughness scenarios. We find that, via transitional ABL dynamics, aeolian sediment aggradation can be influenced by roughness both inside and outside dune fields.
Publisher: Wiley
Date: 30-01-2014
DOI: 10.1111/PPA.12182
Publisher: Cold Spring Harbor Laboratory
Date: 14-05-2020
DOI: 10.1101/2020.05.12.091827
Abstract: Ascochyta rabiei asexual spores (conidia) were assumed to spread over short distances (∼10 m) in a combination of rain and strong wind. The potential distance of conidial spread was investigated in three rainfall and three sprinkler irrigation events. Chickpea trap plants were distributed at the distances of 0, 10, 25, 50 and 75 m from infected chickpea plots before scheduled irrigation and forecast rainfall events. Trap plants were transferred to a controlled temperature room (20 °C) for 48 h (100% humidity) after being exposed in the field for 2–6 days for rainfall events, and for one day for irrigation events. After a 48 h incubation period, trap plants were transferred to a glasshouse (20 °C) to allow lesion development. Lesions on all plant parts were counted after two weeks, which gave an estimate of the number of conidia released and the distance travelled. Trap plants at all distances were infected in all sprinkler irrigation and rainfall events. The highest number of lesions on trap plants were recorded closest to the infected plots – the numbers decreased as the distance from the infected plots increased. There was a positive relationship between the amount of rainfall and the number of lesions recorded. A generalised additive model was developed that efficiently described spatial patterns of conidial spread. With further development, the model can be used to predict the spread of A. rabiei . This is the first systematic study to show that conidia distribute A. rabiei over longer distances than previously reported.
Publisher: Springer Science and Business Media LLC
Date: 13-05-2014
Publisher: American Geophysical Union (AGU)
Date: 03-2021
DOI: 10.1029/2020GL090924
Abstract: Wind‐blown sand dunes are both a consequence and a driver of climate dynamics they arise under persistently dry and windy conditions, and are sometimes a source for airborne dust. Dune fields experience extreme daily changes in temperature, yet the role of atmospheric stability in driving sand transport and dust emission has not been established. Here, we report on an unprecedented multiscale field experiment at the White Sands Dune Field (New Mexico, USA), where by measuring wind, humidity and temperature profiles in the atmosphere concurrently with sediment transport, we demonstrate that a daily rhythm of sand and dust transport arises from nonequilibrium atmospheric boundary layer convection. A global analysis of 45 dune fields confirms the connection found in situ between surface wind speed and diurnal temperature cycles, revealing an unrecognized climate feedback that may contribute to the growth of deserts on Earth and dune activity on Mars.
Publisher: American Geophysical Union (AGU)
Date: 24-08-2020
DOI: 10.1029/2020GL088919
Abstract: In zones of loose sand, wind‐blown sand dunes emerge due the linear instability of a flat sedimentary bed. This instability has been studied in experiments and numerical models but rarely in the field, due to the large time and length scales involved. We examine dune formation at the upwind margin of the White Sands Dune Field in New Mexico (USA), using 4 years of lidar topographic data to follow the spatial and temporal development of incipient dunes. Data quantify dune wavelength, growth rate, and propagation velocity and also the characteristic length scale associated with the growth process. We show that all these measurements are in quantitative agreement with predictions from linear stability analysis. This validation makes it possible to use the theory to reliably interpret dune‐pattern characteristics and provide quantitative constraints on associated wind regimes and sediment properties, where direct local measurements are not available or feasible.
Location: Australia
Location: Australia
Location: No location found
No related grants have been discovered for Paul Melloy.